crypto: ghash - Add GHASH digest algorithm for GCM

GHASH is implemented as a shash algorithm. The actual implementation
is copied from gcm.c. This makes it possible to add
architecture/hardware accelerated GHASH implementation.

Signed-off-by: Huang Ying <ying.huang@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Kconfig b/crypto/Kconfig
index f2002d8..0ae170e 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -290,6 +290,13 @@
 	  gain performance compared with software implementation.
 	  Module will be crc32c-intel.
 
+config CRYPTO_GHASH
+	tristate "GHASH digest algorithm"
+	select CRYPTO_SHASH
+	select CRYPTO_GF128MUL
+	help
+	  GHASH is message digest algorithm for GCM (Galois/Counter Mode).
+
 config CRYPTO_MD4
 	tristate "MD4 digest algorithm"
 	select CRYPTO_HASH